Four Senate Republicans, including Charles E. Grassley of Iowa, want the details of the immigration overhaul package being drafted behind closed doors by a bipartisan group of eight senators that hopes to unveil its bill next week.

And they want the details on Monday.

Grassley, who is ranking member of the Judiciary Committee, along with committee members Jeff Sessions of Alabama, Mike Lee of Utah and Ted Cruz of Texas, wrote to the four GOP members of the immigration group asking them the make their staffs available to the committee’s GOP staff by no later than Monday evening.

“The time for transparency has come,” Grassley wrote in a letter dated Thursday to GOP Sens. John McCain and Jeff Flake of Arizona, Lindsey Graham of South Carolina and Marco Rubio of Florida.

“Given the Majority’s rushed time table, we believe it is time for you to discuss the status of your negotiations, disclose what concessions have been made and provide details to members of the Judiciary Committee as well as the entire Republican Caucus,” the letter said.

Others have also raised concerns about the bill being drafted behind the scenes, including Judiciary Chairman Patrick J. Leahy, D-Vt.

Nevertheless, Leahy has said he plans to take up the measure as soon as possible, seeking to take advantage of the growing support for revisions, including from the Republican National Committee and Sen. Rand Paul, R-Ky.

However, Leahy has also sought to assure Republicans that he wants an open and transparent process and intends to allow for requisite debate and opportunity amendments, in part, to make sure the process does not become an excuse for opposition of the measure.

Sessions, in particular, has been critical of Leahy and believes he plans to try to ram the bill through committee. In the letter, the four Republicans ask the immigration group to help ensure that their minority rights are preserved as the Senate considers the package.

The four said they “hope you will pledge your commitment to protecting the rights of the minority in the Senate by demanding a full, orderly and open debate process during Committee consideration and when the bill is sent to the full Senate,” the letter said. Rubio has already said he wants a lengthy committee process for the bill.

The group also said it has concerns that Leahy has indicated that he may hold one hearing, given that more than 40 immigration hearings have been held by the panel over the past four Congresses. The group would like, what it argues would be, a more thorough process hearing from a wide variety of experts.

“Going forward, we expect to hear from experts on each of the proposals [within the bill] being put forth, including but not limited to a new temporary workers program, border security, interior and worksite enforcement, and the impact of a large-scale legalization on American workers and taxpayers,’ the letter continued.

“We hope you will stand with us to ensure that all viewpoints are heard before the committee considers any immigration legislation,” the letter said.